1. Field of the Invention
The present invention relates to a liquid applying apparatus and an ink jet printing apparatus, and specifically to a liquid applying apparatus that applies a liquid on a medium such as a print sheet for a predetermined purpose, for example, coagulation of an ink color material, and an ink jet printing apparatus including the liquid applying apparatus.
2. Description of the Related Art
Spin coaters, roll coaters, bar coaters, and die coaters are widely known as methods of applying a liquid or a liquid material on media. These applying methods are based on consecutive applying on relatively elongate applying media. Thus, for example, if applying media of a relatively small size are intermittently conveyed and then applied, applying beads may disadvantageously be displaced at an applying start or end position for each applying medium. Thus, for example, resulting coated films may be prevented from being uniform.
In the field of ink jet printing apparatuses, some known apparatuses use liquid applying mechanisms. For example, a liquid is applied on a print medium, which is then printed. Japanese Patent Laid-Open No. 2005-254229 proposes a liquid applying apparatus and an ink jet printing apparatus which reduce the adverse effect of an increase in the number of times an applying member such as an applying roller is used. The liquid applying mechanism includes a liquid holding member with a groove for liquid holding space in which an applying liquid is held, a liquid supply port through which the applying liquid is supplied to the groove, and a collection port through which the applying liquid is discharged from the liquid holding space. The liquid applying mechanism also includes a circulation system with a pump which supplies an applying liquid to the liquid holding space and which discharges the applying liquid from the liquid holding space. A contacting portion of the liquid holding member is biased by a bias force of a spring to contact with a peripheral surface of an applying roller so that the liquid holding member and the applying roller form the liquid holding space. The biasing prevents the applying liquid from leaking inadvertently from the liquid holding space while the applying roller is rotating or stopped. Rotation of the applying roller allows the applying liquid held in the liquid holding space to spread all over the peripheral surface of the roller. The applying liquid is thus transferred to and applied on the medium. Furthermore, the rotation of the applying roller allows the applying liquid remaining on the applying roller after the transfer to the medium to be collected in the liquid holding member.
For the above-described mechanism that applies the liquid using the liquid holding space formed by the liquid holding member and the applying roller, the contacting relationship between the liquid holding member, in which the applying liquid is contained, and the applying roller is relatively important matter. For example, the liquid holding member desirably abuts against the applying roller under a uniform pressure to appropriately keep the liquid holding space closed. On the other hand, during the applying of the liquid, an appropriate amount of applying liquid is desirably evenly applied on the medium by the rotating applying roller.
In the field of ink jet printing apparatuses, an apparatus described in Japanese Patent No. 3593795 is known as a technique that takes into account a contacting pressure of such a roller as described above. To maintain parallelism between a feeding roller and a pinch roller that presses the print medium against the feeding roller to exert a frictional conveying force, Japanese Patent No. 3593795 includes a mechanism that aligns rotating center shafts of the feeding roller and the pinch roller so as to place the rotating center shafts parallel to each other. Thus, the pressure under which the pinch roller abuts against the feeding roller can be made uniform.
However, in such a conventional liquid applying mechanism as described in Japanese Patent Laid-Open No. 2005-254229, the contacting relationship between the liquid holding member and the applying roller may be insufficient. More specifically, with the conventional configuration, which maintains the contacting relationship simply by the biasing with the spring, a uniform contacting pressure cannot be maintained unless a relatively accurate positional relationship is established between the liquid holding member and the applying roller. If the uniform contacting pressure fails to be maintained, the applying liquid may leak from the liquid holding member.
Furthermore, when the applying roller rotates to perform an applying operation, a liquid holding member desirably tightly contacts the applying roller on a side of the liquid holding member from which the applying liquid flows out, in order to evenly spread the applying liquid on the applying roller. On the other hand, during the applying operation, on a collection side of the liquid holding member, the applying liquid is desirably likely to flow into the liquid holding member. In contrast, such an applying mechanism as described in Japanese Patent Laid-Open No. 2005-254229 maintains the contacting relationship simply by the biasing with the spring. Thus, realizing the above-described behavior of the applying liquid by means of the applying mechanism is difficult.
On the other hand, the roller contacting mechanism described in Japanese Patent No. 3593795 includes the alignment mechanism aligning the rotating shafts of the two rollers, in addition to the biasing by the spring. Thus, applying of this contacting mechanism to the liquid applying mechanism described in Japanese Patent Laid-Open No. 2005-254229 allows the positional relationship between the centers of the liquid holding member and the applying roller to be accurately maintained. However, even a slight deviation in the bias direction of the spring hinders prevention of the contacting portion of the liquid holding member from contacting unevenly against the applying roller, as shown by a dashed line in FIG. 11. As a result, the closing force of the liquid holding member may become nonuniform.
Furthermore, if the mechanism in Japanese Patent No. 3593795 is used, the alignment mechanism needs to have loose fitting so as to enable automatic alignment. Thus, when the applying roller rotates forward or backward, the liquid holding member moves in conjunction with the rotating applying roller. In this case, when the liquid holding member moving in conjunction with the applying roller is stopped, the applying liquid may leak from the liquid holding space.